1. Field of the Invention
The present invention relates to an optical data access apparatus and method for controlling an optical pick-up.
2. Descriptions of the Related Art
In these days, more and more people like to use optical data access apparatus, such as an optical disc drive, to access data on a optical disc, for it has advantages of large storage capacity and small size. A conventional optical disc drive comprises a spindle, a signal processing unit (SPU), a digital control unit (DCU), an optical pick-up (OPU), and a central processing unit (CPU).
When the optical disc drive is activated to access the data on an optical disc, the spindle rotates the optical disc and the OPU emits light, receives the reflected light from the optical disc and transmits signals to the SPU. The SPU then converts the signals into a plurality of servo signals, such as a focus error (FE) signal, a tracking error signal, a RF signal and/or a defect signal. These servo signals are analyzed by the CPU. If the light does not focus on the desired position, the CPU controls the DCU to generate a control signal to make the OPU adjust the light focus continuously until the light focuses on the desired position. This is so-called a focus-search period. Once the CPU determines that the light will focus on the right position for a period of time (a focus-on detection period), the optical disc drive enters a focus-on period and the data on the optical disc can be accessed correctly.
FIG. 1 shows a time diagram to specify the aforementioned periods, wherein the servo signal is the RF signal 202. During the focus-search period 11, the OPU is controlled to approach the optical disc, and the RF signal 202 becomes larger and larger while the focus of the light gets closer to the desired position. Once the RF signal 202 is larger than a threshold level 204, the optical disc drive judges that the focus of the light is close to the desired position. Then the optical disc drive determines whether the light keeps focusing on the desired position for the period of time. This is the focus-on detection period 12. If yes, the optical disc drive enters the focus-on period 13 and the OPU may access data from the optical disc correctly.
During the focus-on detection period 12, the OPU keeps moving toward the optical disc because of inertia, and the probability of hitting the optical disc is high. This causes the damages of the OPU as well as the optical disc.
During the focus-on period 13, it is possible that the OPU is forced to move toward the optical disc directly to do keep focusing if the light suddenly fails to focus on the desired position. Referring to FIG. 2, then the RF signal 202 goes below a threshold level 206, the CPU judges that the focus of the light is far from the desired position. And the CPU determines whether the light focus drop from the desired position for a period of time, that is the so-called focus-drop detection period 22. If the RF signal 202 goes below the threshold for the focus-drop detection period 22, the optical disc drive enters a focus-drop period 23. Similarly, if the OPU hits the optical disc due to its inertia, this also causes the damages of the OPU and the optical disc.
Therefore, a solution for preventing the OPU of an optical data access apparatus from hitting a disc is needed in this field.